Evaluation of precipitation phase and mechanical properties according to aging heat treatment temperature of Inconel 718
Gang Ho Lee, Minha Park, Byoungkoo Kim, Byoungkoo Kim, Jong Bae Jeon, Sanghoon Noh, Byung Jun Kim, Byung Jun Kim
Abstract
In recent years, the demand for high strength materials such as aerospace, offshore plant, energy, and manufacturing has increased due to the need for stability and reliability in severe environments. Especially, Inconel 718, a nickel-based superalloy with excellent high strength properties, is widely used. Inconel 718 undergoes a two-step process, including solution heat treatment and aging, to control its mechanical properties. The alloy's strength relies on precipitation phases like MC carbides, Gamma prime (γ′), and Gamma double prime (γ'´), influenced by aging conditions. In this study, we tried to investigate the correlation between the behavior of precipitates and mechanical properties according to the primary aging heat treatment temperature. In addition, the precipitation hardening of Inconel 718 according to various aging heat treatment conditions was investigated through various analysis such as microstructure, SEM, EDS and TEM. The highest strength and hardness, coupled with reduced impact toughness, were observed after heat treatment at 718 °C due to an increase in the size and quantity of γ′ and γ'´ precipitates. In addition, as a result of fracture surface analysis of the Charpy impact test specimen, intergranular fracture was observed due to abundant small-sized precipitates formed within the boundary.